By Alexandra Goho
The Stem Cell Hypothesis
Could a small number of self-renewing cancer cells be at the root of breast cancer?
By Alexandra Goho
Much of the discussion surrounding stem cells today is focused on the promise of using these powerful cells to treat such diseases as diabetes and Parkinson’s, or to repair damaged tissue—say, after a heart attack. But stem cell biology is also making inroads in another important area: breast cancer research.
Although the hypothesis is still somewhat controversial among oncologists, the real culprit in the disease may be a small subpopulation of cells called cancer stem cells, according to a growing body of evidence over the last decade. “The field has exploded. It’s really been exciting,” says Jeffrey Rosen, a developmental biologist at the Baylor College of Medicine in Houston.
In a tumor (mass of abnormal cells above, on a breast duct) cancer stem cells (green) may be more resistant to chemotherapy (yellow) and radiation than normal cancer cells (brown). [Art: Nicolle Rager Fuller]
Generally speaking, stem cells are unique cells in the body that have the ability to self-renew and to give rise to a range of specialized cell types, such as heart cells, immune cells and neurons. These potent cells are critical during development and in helping the body heal itself after an injury, for instance.
Researchers believe cancer stem cells are one of two things: normal stem cells that have gone awry, or more specialized cells that have somehow acquired stem cell–like properties, including an uncontrolled capacity to self-renew. Many researchers believe that only cancer stem cells, which represent a tiny fraction of an entire tumor, have the intrinsic capacity to initiate cancer and fuel tumor growth. They may also underlie resistance to standard therapies. If the theory holds true, it could fundamentally change the way doctors diagnose and treat breast cancer.
The first study to show that cancer stem cells can initiate cancer was published in 1994. John Dick, a molecular biologist at the University of Toronto, succeeded in isolating cancer stem cells from patients with human acute myeloid leukemia. When he and his colleagues transplanted the cells into mice, the animals developed the disease. In contrast, mice that received other leukemia cells did not. In 2003, another group of researchers found cancer stem cells in breast cancer—the first evidence of the cells in a solid tumor. Led by cancer biologists Michael Clarke and Max Wicha at the University of Michigan in Ann Arbor, the researchers transplanted cancer stem cells from human breast tumors into mice. Once again, the malignant stem cells reconstituted tumors in animals but the other cancer cells did not. Since then, cancer stem cells have been found in a variety of cancers, including brain, prostate and pancreatic cancer.